Cavity resonator circuit



March 9 1954 N. c. c'oLBY CAVITY RESONATOR CIRCUIT Filed June 1, 1951 Sgm w N R S Patented Mar. 9, 1954 STE cAvITY aEsoNA'roa cinourr Norman C. Colby, Mount Helly, N. J., assigner to Radio Corporation of America, a corporation of Delaware 11 Claims. 1

The present invention is related to electron tube circuits and more particularly to high frequency electron tube circuits employing cavity resonators. Y

It is frequently desirable in tube circuits to couple the output of one tube circuit taken from the grid-anode circuit or gridcatliode circuit to the input (cathode-grid circuit) of another tube circuit. IThis has been accomplished heretofore by coupling a cavity resonator' circuit to the output of one tube and another cavity resonator cir* cuit to the input of another tube and coupling the two resonators. More generally, where it is desired to couple the output of a tube, whether the output is taken from the cathode-anode circuit or the anode-grid circuit, to the input or cathode-grid circuit of another tube, it is customary to employ separate resonators for each tube. This arrangement has a tendency to taire up space and it is, desirable to simplify the arrangement and make it more compact. Compactness also lends itself to easy cooling of the tubes. It is also desirable to make the coupling arrange-A ments simple and easily tunable over a wide range.

It is an object of the present invention to couple the output of one tube to the input of another tube by a simple arrangement.

It is another object of the invention to provide asimple arrangement coupling the output of one tube to the input of another at extremely high frequencies where cavity resonators may be einployed to advantage.

A further object of the invention is to provide a coupling arrangement from the output of one tube to the input of another which is compact, readily constructed, and easily tuned over a wide tuning range.

A still further object of the invention is to couple the grid-anode circuit of one tube to the cathode-grid circuit of another tube.

Another object of the invention is to provide a coupling arrangement of the type described in which the tubes may be readily cooled.

In accordance with the invention a single cavity resonator is coupled between the output of a tube,- whether the anode-cathode circuit or the grid"- anode circuit, and the input of a second tube, that is, the cathode-grid circuit thereof. Preferably', rectangular cavity resonators are employed with a tuning slug or screw centrally located in the resonator. These central tuning slugs provide a very broad range of tuning linear with frequency. The two tubes coupled to the resonator are in; serted therein, the circuit between two electrodes of the same tube (whether the input or output circuit), being coupled by connecting these tivo electrodes to opposite resonator walls. The tubes are inserted off-center and preferably on opposite sides of the centrally located tuning element.` By this means the connections to several tubes may be cas'caded in an especially compact and desirable arrangement, and also the advantages of a broad tuning range secured.

The foregoing objects, and other objects, advantages, and novel features of the invention will be more apparent from the following description when taken in connection with the accompanying drawing, in which like reference numerals refer to like parts, and in which:

`Eig. 1 is a block diagram schematically repree senting a repeater system; and

Fig. 2 is a cross-sectional View of a preferred embodiment of the invention employed in the sys-` tem oi `liig. l and comprising an oscillator tube and a cavity resonator circuit coupled to a mixer tube and another cavity resonator circuit coupling the mixer tube to an amplifier output tube.

Referring to Fig. l., there is illustrated a re' pea-ter link in a radio communication system. l A receiving antenna l Ill receives a signal at 1,970 megacy'cles per second (MCS) which is applied to an input mixer H2. Mixer i I2 also receives sig-Y nals from a local oscillator l ld at 2000 MCS. The difference signal of 3D MCS from input mixer I I2 is fed to a 30 MCS amplifier H6 Where it is 'am-1 plified. After amplification the 30 MCS signal is supplied to a mixer I l 8 called here the frequency shift mixer. To the frequency shift mixer H8 is also supplied a io MCS signal from an oscillator I2@ called here the frequency shift oscillator@ Thefrequency shift mixer provides a sum signal ofthe 40 MCS and 30 MCS inputs to it, of `'T0 MCS which is ampliiied in a 70 MCS amplie'r I 22. The 7G MCS output of the 70 MCS amplier 122 is applied to still another mixer I2ii,.called here the final mixer. The nal mixer IZA develops a difference signal of 1930 MCS which is 'supplied to a 1,930 ulILCS ainpliier 26 and which, after amplification, is fed to a transmitting antenna Hi8. I

The input signal frequency of 1970 MCS is thus beat down for amplication, and the output is 40 MCS below the input, to avoid self oscillation of the repeater link caused by pick-up at the receiv'ing antenna lil! from the transmitting an;- tenna |28. The oscillator frequencies may be the same for different repeated stations, and the two oscillators I Id, IZB, may be standard system components. At the next repeater Station or link, if there is one, the input signal is, of course, 1,930 MCS, the input mixer supplies a 30 MCS beat signal, the frequency shift mixer supplies a 70 MCS output, and the transmitted signal is again 1,970 MCS. A system of this type is described in the copending application of Leland E. Thompson for Relay System, Serial No. 205,685, filed January l2, 1951, and also in the copending application of Benjamin F. Wheeler, for Relay System, vSerial No. 211,942, iiled February 20, 1951, now Patent No. 2,653,315.

The dotted lines of Fig. 1 enclose a portion |30 of the system which embodies the invention and is illustrated with greater particularity in Fig. 2.

A tube Ill having an anode I2, a control grid or electrode I4 and a cathode I6 serves as an oscillator tube for the local oscillator II4. The oscillator tube I is inserted in an oscillator anode circuit cavity resonator I8. The oscillator anode circuit resonator I8 is rectangular and preferably resonant at the 2000 MCS operating frequency in the TEu,1,1 mode. A tuning screw 20 is inserted centrally of the resonator I8. The tube I0 has its anode inserted in an aperture 22 in one wall 24 of the resonator I8. Contact between the anode I2 and an annular disk 22a is made by spring finger contacts 26. The annular disk 22a is insulated from the wall 24 by an annular mica spacer 24a. This disk 22a affords suiiicient capacity that the anode is virtually connected to the wall 24 at 2000 MCS but insulated therefrom for direct current (D. C.) voltages. The control electrode I4 makes contact directly with the wall 28 opposite wall 24 of the anode circuit resonator I8, spring fingers 38 serving to effectuate this contact through a cylindrical skirt 32. The oscillator tube I0 extends through an aperture 34 in the wall 28. The oscillator tube cathode I6 is located in a second resonator 36 designated as the oscillator cathode grid resonator. A cathode skirt 38 is effectively in contact at 2000 MCS with a wall 40 opposite the wall 28 of the anode circuit resonator, but insulated therefrom for D. C. or very low frequency voltages.

The cathode arrangement is somewhat similar to that of the anode. An insulating spacer is placed between the wall and a disc-like apertured capacity plate 44 has spring fingers directly in contact with cathode skirt 38. The metallic disc 44 is connected to the cathode leads to effect a high capacity coupling and substantially a shortcircuit at the 2000 MCS operating frequency to the outside of the wall 40. Cathode contact may be made to the disk 44. The tube type is 2039A. As the other tubes to be described are inserted in similar manner, they need not be described with the same particularity. The oscillator cathode-grid resonator 36 is also a rectangular cavity resonator operating in the same mode and tunedto the same frequency as the oscillator anode circuit resonator I8. The cathode-grid resonator 36 has a tuning slug 46 insertedcentrally thereof. A feedback coupling loop 41 couples the two oscillator cavity resonators through an aperture 28a in a common wall portion of wall 28.

A mixer tube 48 serving as the final mixer I24 has its cathode grid circuit coupled to the oscillator cathode grid resonator 36 by insertion through aligned apertures. The aligned apertures and mixer tube 48 are on opposite sides of the centrally located tuning slug 20 in the cathode grid resonator 36 from oscillator tube I0. The mixer tube 48 includes an anode 58, control electrode 52, and a cathode 54. 'Ihe control electrode 52 is connected by spring fingers 68 to the wall 58. The cathode 54 has its connection by spring ngers 56 to a disk 51 capacity coupled to the wall 40 of the oscillator cathode grid resonator 36, the arrangement being similar to that of the oscillator tube cathode connection. The wall portion 58 is an extension of the wall 28 and is a common wall portion between the cathodegrid resonator 38 and a mixer resonator 60. Wall 62 of the mixer resonator opposite the wall portion 58 is a continuation of the wall 24 of the anode circuit resonator I8. The oscillator anode circuit resonator I8 and the mixer resonator 60 have the wall 64 in common. The anode 50 of the mixer tube 48 is capacitively coupled to the wall 62 by contact with spring ngers 66 connected to annular disk 61. The mixer tube 48 is inserted through suitably aligned apertures in the wall portions of the mixer resonator 6U. A tuning screw 10 is inserted centrally of the mixer resonator 60. The mixer tube 4B is off-centered in the mixer resonator 60, on one side of the tuning screw or slug 10. An amplifier tube 12 is inserted with its cathode-grid circuit coupled to the mixer resonator 60; the aligned apertures through which the amplifier 12 is inserted in the mixer resonator 60 are off-centered and on the opposite side of the central axis and tuning slug of the cavity resonator from the location of the mixer tube 48.

The 1930 MCS amplifier I26 includes an amplifier output cavity resonator 14 which has a portion of one wall 16 in common with the wall 58 of the mixer resonator and another wall 11 altogether in common with the oscillator cathode grid-resonator 36. The remainder of the output resonator one wall 16 is an extension of wall 58. Another wall 18 of the amplifier resonator 14 opposite wall 16 is an extension of wall 40 opposite wall 58 of oscillator cathode-grid resonator 36. A tuning screw is provided centrally of amplifier resonator 14. The output may be taken from an output coupling loop 82 through a coaxial line 84, concealed in the view of Fig. 2 behind the tuning slug 80. The cathode and anode couplings respectively to walls 62 and 18 are similar to the couplings of the like electrodes of the other tubes.

In operation, the local oscillator II4 provides a 2000 MCS signal which is coupled by the oscillator cavity resonator to the cathode grid circuit of the mixer tube 48. The mixer tube 48 also has applied to its cathode the '10 MCS signal, by a connection to the annular disk 51. Itis understood that a common ground connection, designated on one of the resonator walls, is not otherwise shown. There is thus impressed on the cathode-grid circuit of mixer tube 48 two signals, one of 2000 MCS from the oscillator, the other of rI0 MCS from the 70 MCS amplifier I22 of Fig. 1.

The mixer tube 48 by its non-linearity of response, and having both the oscillator and incoming voltages applied to its grid circuit, develops the difference frequency voltage of 1930 MCS in its output, across the grid-anode circuit. The mixer resonator 60 is tuned to this difference frequency of 1930 MCS which is thus applied to the cathode-grid circuit of amplifier tube 12, is amplified thereby, and applied to the amplifier or output resonator 14. The amplified diierence or intermediate frequency of 1930 MCS is then taken from the output loop 82 and coaxial cable 84 to the transmitter antenna |28 of Fig. 1, or it may be further amplified. For this purpose, if

5.. desired, it is now apparent that a further chain of resonators and tubes may be connected in manner similar to that already shown, using the resonators for tube coupling. In that event, of course, the output coupling loop 82 and cable 84 may not be connected to the amplifier resonator 16.

lOne highly useful feature resides in the slot-r ting of the resonator walls. These slots, for example, slots 'Vla in the narrow wall 1'! seen in the view of Fig. 2, have their length along lines of current, so that they interfere very little with the current distribution of the resonators. Similar slots (not shown) may be cut in the other Walls. A blower (not shown) may then be located to blow air through the slots into the resonators to assist in cooling the tubes. If such slots are located in common wall portions, as for example 11a in the wall 11, it is possible to feed air into one resonator, for example 60, and then feed it through slots in the walls to an adjacent resonator. Only one blower may then serve several tubes. VCooling of the tubes is most important to their long life and particularly to their successful use when enclosed, as here, in cavity resonators.

Another highly useful feature of the invention disclosed is found in the tuning slugs. It has been found that these slugs, centrally located in one broad wall, give a substantially linear change of the resonator frequency with depth of insertion from the broad wall into the resonator. In effect, the capacity and inductance are being. changed simultaneously. This linearity of tuning is highly desirable. The tuning range has been found to be amazingly great. For example, resonators of the dimensions of 21A by 41/2 by 7a inches have' been tuned from about 1500 to 4000 MCS.

The operating frequencies and cavity resonator dimensions given may be taken as typical of Y a successfully operated embodiment of the invention. The type 2039Av tube has been satisfactorily employed for all the tubes.

One broad wall of each resonator is partially in common with the broad walls of at least one L.

other resonator. Where more than three resonators are connected in tandem, it is apparent that one narrow wall (such as S4 or 11) may be entirely in common with one narrow wall of the third. This latter arrangement is preferred, for reasons of compactness, if the tuning range permits it, but if not, the narrow walls may be only partially in common. The dimension normal to the broad walls may be termed the depth of the rectangular resonator. The other dimensions of the narrow walls are the frequency determining dimensions in the TEo,1,1 mode. In rectangular cavities operated in the TE0,1,1 mode the tubes are inserted through apertures in the broad walls so that the electron streams are parallel to the electric fields and interact therewith.

It is apparent that there is disclosed herein a novel, particularly compact, and conveniently constructed arrangement for coupling tubes through cavity resonators.

What is claimed is:

1. A cavity resonator circuit comprising a pair of cavity resonators each having a pair of opposed walls, one of said walls having a portion less than the whole in common with a wall portion of the other resonator less than the whole, a tube having electrodes one coupled to said common wall portion and each of the others being coupled respectively to the said wall of each resonator opposed from the wall having the common wall portion, a second tube having elec trodes coupled to said opposed walls of one" said resonator at a point displaced from and at anlother wall portion than said common wall portion, and resonator turning means in said one resonator positioned along a central axis of said opposed walls.

2. A cavity resonator circuit comprising a pair of cavity resonators each having a pair of op; posed walls, one of said Walls having a portion less than the whole in common with a Wall portion of the other resonator less than the whole, a tube having electrodes one coupled to said come mon wall portion and each of the others being coupled respectively to the said wall of each resonator opposed from the wall having the coma mon wall portion, a second tube having' electrodes coupled to said opposed walls of one said resonator at a point displaced from and at am other wall portion than said common wall pori tion, and said opposed walls of said one resonator having a single central axis, said tubes being posi-4 tioned on opposite sides of said centralr axis, andv resonator tuning means in said one resonator positioned along said central axis.

3. A cavity resonator circuit comprising a pair" of cavity resonators each having a pair of opposed broad walls with respect to which the elec-` tric vector is normal in the operating mode and' each having a central axis normal to said walls, one axis being displaced from the other, one of said resonators having one broad wall with" one" fractional portion less than the whole thereof in common with a broad wall portion of the` other said resonator, a tube having electrodes coupled respectively to said common wallporl tion and to the broad walls of each' resonator on one side of said axisof said one resonator and a second tube having electrodes coupled respectively to the other fractional portion of said one broad wall of said one resonator and the opposedl broad wall thereof, on the other side of the axis of said one resonator from said first tube, and resonator tuning means in said one resonator positioned along said one central airis, whereby the two resonators are coupled together by the first tube, and the two tubes are coupled together by said one resonator.

4. 'Ihe circuit claimed in claim 3, said rst tube electrodes being cathode, control, and anode electrodes, said control electrode being coupled to said common wall portion.

5. The circuit claimed in claim 3, said resonators being rectangular.

6. A cavity resonator circuit comprising three rectangular cavity resonators each having a pair Vof opposed broad walls with respect to which the electric vector is normal in the operating mode and each having a central axis normal to said walls, said axes being displaced from each other, the rst of said resonators having one broad wall with a fractional portion less than the whole thereof in common with a fractional portion of one broad wall of the second resonator, said one broad wall of said second resonator having a second fractional portion in common with one broad wall of the third resonator, a first tube having electrodes coupled respectively to the broad walls of said rst and second resonators Where said rst and second resonators have their common wall portion, and a second tube having electrodes coupled respectively to the broad walls of said second and third resonators Where said second and third resonators have their common wall portion, whereby said first tube couples said 7 rst and second resonators, said second resonator couples said tubes, and said second tube couples said second and third resonators.

7. The circuit claimed in claim 6, said tubes being on opposite sides of said second resonator axis.

8. The circuit claimed in claim 6, said first and third resonators each having one side wall normal to said broad walls and in common with said one side wall of the other.

9. A cavity resonator circuit comprising four rectangular cavity resonators each having a pair of opposed parellel broad walls with respect to which the electric vector is normal in the operating mode and each having a central axis normal to said walls, said axes being parallel and displaced from each other; the first said resonator` having one broad wall a fractional portion less than the whole of which is in common with a fractional portion less than the whole of one broad Wall of the second, a diierent portion or said second resonator one Wall being in common with a fractional portion less than the whole of one broad wall of the said third resonator, and a different portion of said third resonator one wall being in common with a fractional portion less than the whole of one broad wall of said fourth resonator; three tubes each having cathode, control, and anode electrodes along respective axes parallel to said resonator axes, said rst tube electrodes being coupled respectively to said rst and second resonator broad walls with said control electrode coupled to their common wall portion; a feed-back coupling between said first and second resonators; said second tube having its cathode electrode coupled to the other broad wall of said second resonator, its said control electrode coupled to said common wall portion between said second and third resonators, and its said anode electrode coupled to the other broad wall of said third resonator; said third tube having its cathode electrode coupled to the other broad wall of said third resonator, its control electrode coupled to said common wall portion between said third and fourth resonators, and its said anode electrode 8 to the other broad wall of said fourth resonator, means to apply an input voltage to said second resonator independently of said tubes, and means to take the output voltage from said fourth resonator.

10. A cavity resonator circuit comprising three cavity resonators each having a pair of opposed walls with respect to which the electric vector is normal in its operating mode and each having a. central axis normal to said broad walls, said axes being displaced from each other, the rst of said resonators having one of said opposed walls with a fractional portion less than the whole thereof in common with a fractional portion of one of said opposed walls of the second resonator, said one Wall of said second resonator having a second fractional portion in common with one of said opposed walls of the third said resonator, a first tube having electrodes coupled respectively to the said opposed walls of said first and second resonators where said first and second resonators have their common wall portion, and a second tube having electrodes coupled respectively to the said opposed walls of said second and third resonators Where said second and third resonators have their common wall portion, whereby said rst tube couples said rst and second resonators, said second resonator couples said tubes, and said second tube couples said second and third resonators.

11. The circuit claimed in claim 10, said opposed walls being broad walls of each said resonator, and being planar and parallel to each other.

NORMAN C. COLBY.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,106,771 Southworth Feb. 1, 1939 2,153,728 Southworth Apr. l1, 1939 2,421,635 McArthur June 3, 1947 2,431,273 Nergaard Nov. 18, 1947 2,451,240 Rosencrans Oct. 12, 1948 2,451,502 Lisman et a1 Oct. 19, 1948 

